The present invention relates generally to a mowing apparatus of the reciprocating sickle type and more particularly to a hold-down with improved adjustment characteristics.
The general mode of operation of reciprocating sickle bar mowing apparatus is well known, as is the importance of keeping the sickle bar knife sections substantially parallel to the ledger surface on the guards, and maintaining the proper clearance between them for good shearing action. Some form of hold-down clip or plate extending over the knife sections is generally used for this purpose.
Heretofore known hold-down mechanisms, such as those shown in U.S. Pat. Nos. 3,490,215, 3,577,716, 4,012,891, 4,894,979 and 6,305,154 are widely used, but have not been entirely satisfactory. The difficulty of adjusting such mechanisms often results in mowers being operated with improper knife clearance. Too much clearance allows crop material to force the knife section away from the cutting edges of the guards, greatly reducing cutting efficiency. Too small a clearance results in drag on the sickle bar assembly and a resultant increase in wear rate and power requirements. For the older clip-type hold-downs, adjustment is generally accomplished by bending the forward portion of the hold-down clip up or down as required, by using a hammer. This method is time consuming and inconvenient, and usually requires removal of the sickle bar so that the adjustment must be checked by means of a gauge rather than by direct measurement with the knives in place. Some attempts at improvement of this type of hold-down clip have involved pivoting the clip in a cradle mounted on the frame member and providing screw-type adjusting means so that the clearance between the forward part of the clip and the sickle section can be varied.
Both the conventional hold-down clip and the screw adjusted versions are typically placed between guards where they suffer additional dual disadvantages—first, of being located so as to snag crop material divided and deflected into this area by the guards, and second, of having only an indirect effect in controlling knife clearances in that they are not directly above the guard ledger surfaces.
Other attempts at improvement have included a variety of less conventional designs including some in which the hold-down plate itself is a form of leaf spring or is spring loaded so that there is always hold-down pressure on the knife sections although, typically, means are provided for adjusting this pressure. This type of hold-down clip is in constant contact with the knife sections and the drag between them increases wear rate and the power required to operate the mowing apparatus.
In another design, the hold-down clip is centered on the guard and clamped in position with the same screw fastener that retains the guard. Typically, screw adjustment is provided to raise or lower the forward part of the clip, but before the screw adjustment can be made, the screw fastener must be loosened to permit pivoting of the hold-down clip, consequently loosening the guards and upsetting adjustment of the wear plates between the sickle bar assembly and the frame member.
It would be quite advantageous to have an adjustment mechanism that does not require removal of components, hammering, or the loosening of hardware to accomplish appropriate adjustments.